Guessing the availability of these future large Sigma telephoto lenses is a year off or more. Regarding their optical or overall quality...it won't matter to some photogs how good these are. They still won't be up to Canon's level in their minds. Sigma is simply a red-headed stepchild, only worthy of scorn. As constant and eternal as the tides...and it's especially true if the Sigma lens costs less than the similar Canon model.
I'm considering purchasing three lenses over the next couple of months, and none of them are made by Canon...but these will be used on a Canon camera. One of these is a Sigma, the 35mm...the others Rokinon and Tamron. The only brand of these which I have no personal experience with yet, is Tamron.
I currently own three canon lenses, one Voigtlander, and one Sigma...and have bought and sold several other Sigmas in the past. The only lens I've ever used that was (slightly) "decentered" was a Tokina. The only time I've been published (so far), was using a Sigma lens...a rather critically maligned one at that. It was still practically Zeiss-level optically, compared to the absurd Canon 18-55 kit lens it replaced. I sold that Sigma for the same price I paid for it, new...after owning it for three years. The buyer was overjoyed to get it! Apparently word got out how good a value it was, especially after it was replaced with an optically inferior model with "OS".
I've never used a Sigma lens with a painted finish...but Sigma is not the only brand who has painted their metal lenses in the past...and then the paint flakes off. That's why most modern DSLR lenses don't have a painted finish, nowadays...